#include<stdio.h>
#include<math.h>
int main()
{
	int i,n;
	float tn,s;
	s=1;
	i=1;
	while(tn>0.00000001)
	{
		tn=(float)(2*n+1)/(pow(2,i));
		s=s+tn;
		i++;
	} 
	printf("%0.8f \n",s);
}
